Stage 2 of the Cambrian is the unnamed upper stage of the Terreneuvian series. It lies atop the Fortunian and below Stage 3 of the Cambrian. It is commonly referred to as the Tommotian, after the Cambrian stratigraphy of Siberia. Neither the upper nor lower boundary has yet been defined by the International Commission on Stratigraphy. Proposals for the lower boundary are the appearance of Small Shelly Fossils, an archaeocyathid species or the mollusc Watsonella crosbyi around 529 million years ago. The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.
Possible candidates for a GSSP include the first appearance of Watsonella crosbyi in the Zhujiaqing Formation in Yunnan, China or the Pestrotsvet Formation near the Aldan River on the Siberian Platform.
- ^ Kouchinsky, Artem; Bengtson, Stefan; Missarzhevsky, Vladimir V.; Pelechaty, Shane; Torssander, Peter; Val'kov, Anatolij K. (24 September 2001). "Carbon isotope stratigraphy and the problem of a pre-Tommotian stage in Siberia". Geological Magazine. 138 (4). doi:10.1017/S0016756801005684.
- ^ a b c "GSSP List ICS". ICS. Archived from the original on 15 November 2012. Retrieved 9 November 2012.
- ^ Li, Guoxiang; Zhao, Xin; Gubanov, Alexander; Zhu, Maoyan; Na, Lin (1 April 2011). "Early Cambrian Mollusc Watsonella crosbyi: A Potential GSSP Index Fossil for the Base of the Cambrian Stage 2". Acta Geologica Sinica - English Edition. 85 (2): 309–319. doi:10.1111/j.1755-6724.2011.00400.x. Retrieved 10 November 2012.